1. Field of the Invention
The present invention generally relates to a surface acoustic wave device, a package for the device, and a method of fabricating the device.
2. Description of the Related Art
As electronic apparatuses with higher performances have become smaller in size, electronic devices to be mounted to such apparatuses are also expected to be smaller and have higher performances. Especially, surface acoustic wave (SAW) devices to be used as electronic parts such as filters, delay lines, and oscillators for electronic apparatuses that transmit or receive electric waves have been required to have downsized packages and high performance.
The conventional SAW device has a SAW chip, which is hermetically sealed in a cavity. The SAW chip has a piezoelectricity device substrate (hereinafter, referred to as piezoelectric substrate) on which interdigital transducers (hereinafter referred to as IDT) having comb-like electrodes are formed. This type of the SAW device is described in, for example, Japanese Patent Application Publication 2001-53577, particularly, FIG. 3). The IDT on the input side converts an electric signal applied thereto into a SAW, which propagates on the piezoelectric substrate. The IDT on the output side converts the received SAW into an electric signal that has been subjected to a given modulation.
A description will now be given of a conventional SAW device 100 with reference to FIGS. 1 and 2. FIG. 1 is a perspective view of the SAW device 100, and FIG. 2 is a sectional view taken along a line A–A′ shown in FIG. 1.
Referring to these figures, the SAW device 100 has a package 102 having a cavity 104 in which a SAW chip 120 is housed. Metal patterns, which include IDTs 122, interconnection lines 124, and electrode pads 123, are formed on a circuit-formed surface (main surface) of the piezoelectric substrate 121. The bottom surface of the cavity 104 (die-attached surface) is provided with metal patterns, which include electrode pads 109 aligned with the electrode pads 123 of the SAW chip 120. The SAW chip 120 is flip-chip mounted on the die-attached surface in the facedown state by using metal bumps 112. Thus, the package 102 and the SAW chip 120 are electrically and mechanically connected to each other. The electrode pads on the die-attached surface are electrically connected to foot patterns 114 formed on the bottom surface of the package 102 (opposite to the surface defining the cavity 104) through interconnection lines and via interconnections.
The cavity 104 is hermetically sealed with a metal cap 103 with high reliability. The cap 103 may be fixed to the package 102 by a bonding member 106 (called washer in the following) made of solder or metals such as gold and tin. A metal plating layer 105 is formed on a portion of the package 102 to which the cap 103 is attached. The metal plating layer 105 is electrically connected to a ground foot pattern 113 on the bottom surface of the package 102 via interconnection lines 110 and vias 111 formed in the package 102.
A conventional fabrication method uses a wafer or multiple-package substrate having multiple SAW devices arranged in rows and columns. The multiple-package substrate is divided into individual packages, each having the above-mentioned structure by dicing or scribing.
In the conventional fabrication process, the multiple-package substrate is divided into the individual chips so that the sidewalls of the packages stand vertically. Thus, there is only a small margin of sealing the top surface of the package 102 with a lid member or the like.
There is another problem that occurs in transportation of the SAW devices 100. As shown in FIG. 3, multiple SAW devices 100 are placed in an embossed tape 200 sealed with a cover sheet 210. A problem frequently occurs in which the SAW devices 100 having the vertical sidewalls are not accommodated in recess sections 201 in position. In practice, some SAW devices 100 bite into the embossed tape 200 or deform the sheet 210. It is difficult to remove the SAW devices 100 that have bite into the embossed tape 200 therefrom.